1. Field of the Invention
This invention relates generally to a heat treatment apparatus and more particularly relates to an improved heat treatment apparatus which is suitable for use with a semiconductor manufacturing apparatus.
2. Description of the Prior Art
In a manufacturing process of semiconductor elements there are generally treating processes employing a so-called horizontal heating furnace such as heat diffusion treatment, chemical vapor deposition (hereinafter, simply called as CVD) or annealing treatment. In these treating processes, it is desired that a series of work processes where semiconductor wafers are taken out from casettes, transported into heating furnaces under the state that the semiconductor wafers are arranged with a constant or predetermined interval, and after the treatments, returned into the original cassettes be automatized.
The work process using the prior art apparatus is as follows.
(i) Take out the semiconductor wafers from the cassette by a pair of tweezers;
(ii) Arrange these wafers on a boat with a predetermined pitch by the pair of tweezers;
(iii) Put this boat on a boat receiving base;
(iv) Holding this boat receiving base and carry the boat into a core tube of a furnace;
(v) Catch the boat by a boat insertion bar, operate a boat loader, and insert the boat into the central part of the core tube of the furnace;
(vi) Awaiting that temperature within the core tube of the furnace rises at the original degree because it was lowered by the insertion of the boat, inject gas thereinto and perform the treatments such as diffusion, CVD and so on for the semiconductor wafers; and
(vii) After the treatments being finished, perform the above works in the reverse order of the above as in the order from (v) to (i) and introduce the wafers treated into the original cassette again.
Of these work processes, only the work processes from the boat loader work (v) to the main treatments within the heating furnace (vi) are automatized, but other work processes are all dependent on manual labor in the prior art.
Therefore, the inventor of this invention has previously proposed a semiconductor manufacturing apparatus, in which in the case of manufacturing semiconductor elements all treatment processes employing the horizontal heating furnaces can be automatized.
Now, such previously proposed semiconductor manufacturing apparatus will be described with reference to the drawings.
FIG. 1 shows an overall arrangement of this semiconductor manufacturing apparatus, and this apparatus is arranged so that a series of work processes be automatically controlled by a microcomputer as follows. That is, a plurality of subjects to be treated or semiconductor wafers are taken out from receptacles (cassettes) which hold therein the same, arranged in line with a constant or predetermined space, inserted into a specified heating furnace in which the wafers undergo predetermined treatments (treatments such as diffusion, CVD, and annealing), and thereafter the wafers thus treated are again introduced into the original cassettes. As shown in the figures, this semiconductor manufacturing apparatus includes a control operation section 1 for automatically controlling the afore-described all work processes by the microcomputer, a plurality (twelve, in this example) of receptacles or cassettes 2 (2A, 2B . . . , 2L shown in FIG. 2) with code numbers attached thereon respectively for holding thereon plural semiconductor wafers 3, a treating apparatus 4 having three heating furnaces 4A, 4B and 4C arranged in, for example, the vertical direction, and a transporting apparatus 5 for transporting the wafers 3 between the cassettes 2 and the treating apparatus 4. Each cassette 2 is formed as a box-shape the one of the opposing sides of which are cut away, and into which semiconductor wafers 3 of one lot amount, for example, 25 are arranged with a predetermined pitch (pitch of, for example, 4.76 mm) in the vertical direction in the form of a laminate. As shown in FIG. 2, the plurality of cassettes 2 are arranged in two rows and transported one by one along the directions shown by arrows a, b, c and d intermittently and circularly. When the code number of each of the cassette 2 reaches a position S.sub.0, the code number thereof is recognized by a photosensor D and then the cassette in question is selected. To this end, each cassette 2 has at its side surface with four through-holes 10 bored therethrough which the microcomputer can recognize, whereby the photosensor D comprised of reflection type light-emitting diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 discriminates the portion of the surface of the cassette 2 where the light beam emitted from the photosensor D is reflected from the portion thereof where the light beam therefrom is not reflected thereby producing a hexadecimal signal of 4 bits thus the code number of each of the cassettes 2 being digitized. The portion of each of the surfaces of the cassettes 2 to reflect the light beam is made of metal surface as it is, while the portion which does not reflect the light beam is provided with a black rubber bonded thereon in which the infrared ray emitted from each of the light-emitting diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 is not reflected.
A feeding mechanism 6 for circulating the cassettes 2 includes a pair of feeding nail members 8A and 8B located respectively beneath the two rows of the cassettes 2 and having nails 7 formed integrally thereon at the position corresponding to each of the spaces defined by the adjacent cassettes 2 and a pair of arms 9A and 9B correspondingly provided at both ends of the two rows. In this case, after the feeding nail member 8A was lifted up by a cylinder CY.sub.2 and the respective nails 7 thereof were inserted into the spaces between the adjacent cassettes 2, the feeding nail member 8A is transported by a cylinder CY.sub.1 by the amount of one cassette in the direction shown by the arrow a so that the cassettes 2A to 2F arranged on the one row are pushed by the respective nails 7, transported by the amount of one cassette in the direction a and the cassette 2A reaches the position S.sub.0 thereby. Next, due to the movement of the arm 9A in the direction indicated by the arrow b done by a cylinder CY.sub.8 the cassette 2A located at the position S.sub.0 is transported to the other row, while due to the movement of the arm 9B in the direction indicated by the arrow d done by a cylinder CY.sub.9 the cassette 2G is transported to the adjacent row. Since the feeding nail member 8B is lifted up by a cylinder CY.sub.3 and moved by a cylinder CY.sub.4 in the direction shown by the arrow c, the cassettes 2A, 2L . . . 2H on the other row are similarly transported by the amount of one cassette thus the respective cassettes 2 are transported circularly.
On the other hand, as shown in FIG. 3, the transporting apparatus 5 includes a pitch converting small case 12 for taking out and holding therein the wafers 3 within the cassette 2 designated by the photosensor D with a pitch same as that of the cassette 2 once, an air bearing 13 to transport the wafers 3 sheet by sheet from this small case 12 and a pitch converting large case 14 arranging therein the wafers 3 thus transported in sequence with a predetermined pitch. The small case 12 is located at the position adjacent to and opposing to the cassette 2 brought to the position S.sub.0 and arranged across the air bearing 13 to be movable at every one pitch in the vertical direction through a vertical moving means 15 including a pulse motor M.sub.1. To transfer the wafers 3 between the designated cassette 2 at the position S.sub.0 and the small case 12, over and above the cassette 2 and the small case 12 is provided a transporting mechanism 30; which is comprised of a supporting member 17 to be movable in the up and down direction by a cylinder CY.sub.7 and a pair of arms 16A and 16B supported by this supporting member 17 and to be driven in the opposite directions with each other by cylinders CY.sub.5 and CY.sub.6. In accordance with the transporting mechanism 30, when the wafers 30 are taken out from, for example, the cassette 2 and held in the small case 12, the supporting member 17 is lowered by the cylinder CY.sub.7 and thereafter the cylinder CY.sub.5 is actuated to move the arm 16A in the direction shown by an arrow H. By this arm 16A, all 25 wafers within the cassette 2 are shifted into the small case 12 one at a time. The wafers 3 are transferred from the small case 12 to the cassette 2 by moving the arm 16B by the cylinder CY.sub.8 in the direction shown by an arrow Y.
The pitch converting large case 14 is located at the other end of the air bearing 13 so as to oppose to the small case 12 and arranged thereacross to be movable by one pitch in the vertical direction through a vertical moving means 33 including a pulse motor M.sub.2 and then rotated to be horizontal by a motor M.sub.3 when it reaches the uppermost position. In this case, if a pitch at which the wafers 3 are held therein is set, for example, as 4.0 mm, the large case 14 keeps therein 100 (amounts of four cassettes) wafers 3; at 8.0 mm, 50 (amounts of two cassettes) wafers 3; and at 12.0 mm, 25 ( amount of one cassette) wafers 3, respectively. The wafers 3 are transferred from the small case 12 to the large case 14 as follows; the small case 12 in which the wafers 3 are kept is lowered pitch by pitch to feed the laminated wafers 3 one by one through the air bearing 13 to the large case 14 from the bottom, while the large case 14 is lifted up pitch by pitch in synchronism with the lowering of the small case 12 to take therein the wafers 3 one by one from the top of the large case 14. The transfer of the wafers 3 from the large case 14 to the small case 12 is vice versa, in which the small case 12 is lifted up pitch by pitch from the underside, while the large case 14 is lowered pitch by pitch. In the state under which the wafers 3 have been transferred into the large case 14 completely, each of facets 31 (a portion where part of the wafer 3 is cut away horizontally for ensuring the positioning) of the respective wafers 3 is not located regularly. Therefore the large case 14 is provided at its underside with means 18 for arranging the facets 31 of the respective wafers 3 in line. This means 18 is comprised of a rod-shaped rotatable member 33 which rotatably comes into contact with, for example, the periphery of each of the wafers 3 commonly by a motor M.sub.4. When the respective wafers 3 are rotated by this rod-shaped rotatable member 33, the wafers 3 are detached at their facets 31 from the rod-shaped rotatable member 33, and the rotation of the wafers 3 is terminated whereby the facets 31 of the respective wafers 3 are arranged in line. Moreover, the large case 14 is provided at its underside with a wafer lift 19 which permits all the wafers 3 to be lifted upwardly from the large case 14. Reference CY.sub.10 denotes a cylinder for vertically moving the wafer lift 19.
As shown in FIG. 4, the transporting apparatus 5 further includes a wafer chuck 21 for holding all the wafers 3 kept in the large case 14 and transporting them onto boats 20 of the designated heating furnace 4 (4A, 4B, or 4C). This chuck 21 is arranged movable in the vertical direction by way of a vertical moving means (for example, a feeding screw mechanism and the like) 34 including a pulse motor M.sub.6 and also movable in the horizontal direction by way of a horizontal moving means 35 including a motor M.sub.5. Reference CY.sub.11 designates a cylinder which permits the wafer chuck 21 to open and/or close. In the treating apparatus 4 with three heating furnaces 4A, 4B and 4C, three boats 20 are prepared to correspond to the respective heating furnaces 4A, 4B and 4C. As shown in FIG. 1, these boats 20 are respectively connected with boat loader arms 36A, 36B and 36C and then entered into or got out from the heating furnaces 4A, 4B and 4C by boat loaders 37A, 37B and 37C. In the proximity of the external entrances of the respective heating furnaces 4A, 4B and 4C are respectively provided receiving or holding bases 38 for respectively holding the boats 20. When the boats 20 are inserted into the heating furnaces 4A, 4B and 4C, the receiving bases 38 are laterally moved and then put into the standby state by corresponding cylinders CY.sub.12, CY.sub.13 and CY.sub.14.
Next, the operation of the arrangement made so far will be described.
When a plurality of, in this example, 12 cassettes 2, each keeping therein one lot amount of semiconductor wafers 3 of, for example, 25 ones are transported to the predetermined position as illustrated in FIG. 1, thereafter they are controlled by the microcomputer. First, twelve cassettes 2 are transported one by one by the cassette transporting mechanism 6 intermittently and circularly. When the first cassette 2A is transported to the position S.sub.0, the code number of the cassette 2A is ascertained by the photosensor D. If this cassette 2A is the designated cassette, as shown in FIG. 2, the supporting member 17 is lowered by the cylinder CY.sub.7, the arm 16A is opposed to the cut out side of the cassette 2A and then, the arm 16A is moved by the cylinder CY.sub.5 in the direction shown by the arrow H so as to pass through the cassette 2A thus 25 wafers 3 therein are all transferred from the cassette 2A to the pitch converting small case 12 shown in FIG. 3. Next, the air bearing 13 is actuated to transport the lowermost wafer 3 opposing thereto on the air bearing 13 and it is held in the uppermost portion of the pitch converting large case 14. Thereafter, the small case 12 is lowered at every pitch to supply from the underside the wafer 3 one by one through the air bearing 13 into the large case 14, which is lifted up pitch by pitch, at the pitch of, for example, 4 mm pitch (pitch at which the wafer 3 is kept into the large case 14 can be freely selected by previously designating the pitch at which the large case 14 is lifted intermittently, to be 4 mm pitch, 8 mm pitch, 12 mm pitch and so on).
After the holding of the wafers 3 of one cassette amount was finished, in like manner the wafers 3 of the second, third, and fourth cassettes 2B, 2C and 2D are transported into the large case 14 from the following stage so that totally 100 wafers 3 of four cassettes 2A to 2D are held into the large case 14 as shown in FIG. 5. After all the wafers 3 of the designated cassettes 2 are kept into the large case 14, the large case 14 is rotated to be horizontal by driving the motor M.sub.3 as shown by a one-dot chain line in FIG. 3. Subsequently, the rod-shaped rotatable member 33 is rotated by the motor M.sub.4 and the facets 31 of the respective wafers 3 are arranged in line thereby. Thereafter the wafer lift 19 is lifted up by the cylinder CY.sub.10 thereby lifting all the wafers 3 kept within the large case 14. Next, the wafer chuck 21 on standby at a position S.sub.34 in FIG. 4 is lowered by the vertical transporting means 34 to a position S.sub.31 and grasp all the wafers 3 on the wafer lift 19 by actuating the cylinder CY.sub.11. Thereafter, the wafer chuck 21 is lifted up to the position corresponding to the height of the designated heating furnace (core tube of the furnace), for example, the first heating furnace 4A and, then moved horizontally in the direction shown by an arrow E by way of the horizontal transporting means 35 thus the wafers 3 being put on the boat 20 of the designated heating furnace 4A. At this time, the boat 20 is held on the receiving base 38. After having put the wafers 3 on the boat 20, the wafer chuck 21 is horizontally moved in the direction shown by the arrow H, comes back to the predetermined position S.sub.34 in the vertical direction, and then put into the standby state. After the wafers 3 were put on the boat 20, this boat 20 is inserted into the heating furnace 4A by way of the boat loader arm 36A and the boat loader 37A. In this way, the semiconductor wafers 3 of four cassettes each are respectively inserted into the designated heating furnaces 4B and 4C, in which they will undergo the predetermined treatments such as diffusion, CVD and annealing.
After the treatments, the boats 20 with the wafers 3 put thereon are respectively taken out from the heating furnaces 4A, 4B and 4C each, and thereafter in the perfectly reverse order of the operation upon insertion of the wafers 3, the respective wafers 3 are held into the designated initial cassettes 2. Speaking concretely, first the wafer chuck 21 is operated to grasp the wafers 3 treated in the heating furnace 4C and put them on the wafer lift 19 within the pitch converting large case 14. Then the wafer lift 19 is lowered by the cylinder CY.sub.10 and the wafers 3 are kept into the large case 14 thereby. Thereafter, the wafer chuck 21 is returned to the initial position S.sub.34. The large case 14 are erected by the motor M.sub.3 so as to face the air bearing 13 and the wafers 3 kept within the large case 14 is transported one by one by the subsequent operation of the air bearing 13 to be kept into the small case 12. At this time, the large case 14 is lowered by one pitch each, while the small case 12 is concurrently lifted by one pitch each. Whereas, at the side of the cassettes 2, the cassettes 2 are transported by the cassette transporting mechanism 6 and the code numbers thereof are identified by the photosensor D, whereby the designated cassette, in this case, the cassette 2L is selected and then put into the standby state at the position S.sub.0. After 25 wafers 3 of one cassette amount (that is the amount to be kept into the cassette 2L) were kept into the small case 12, the cylinder CY.sub.7 is actuated to lower the supporting member 17 and then the arm 16B is moved by the cylinder CY.sub.6 in the direction shown by the arrow Y in FIG. 2 thus all the wafers 3 within the small case 12 being transferred into the originally designated cassette 2L to be held therein. In like manner, the next 25 wafers 3 within the large case 14 are put into the cassette 2K and the corresponding wafers 3 are sequentially put into the cassettes 2J and 2I. After the keeping of the wafers 3 in the heating furnace 4C, the same operations as described above are repeated and the wafers 3 in the second heating furnace 4B and the wafers 3 in the first heating furnace 4A are respectively put into the corresponding original cassettes 2.
According to the afore-mentioned semiconductor manufacturing apparatus, in the case of manufacturing the semiconductor elements, all works in the treating processes such as diffusion CVD, annealing and so on using the horizontal heating furnaces, or a series of work processes where the semiconductor wafers are taken out from the cassettes, transported to the heating furnaces under the state that the semiconductor wafers are arranged in line with the constant space or distance, and after the completion of their treatments, they are returned to the original and designated cassettes are carried out automatically. Thus, such advantages are brought about that no-man operation of the apparatus becomes possible, for example, all night long the rate of operation of the apparatus is improved and the number of workers is reduced and so on.
By the way, in such prior art semiconductor manufacturing apparatus, in order to insert the boats 20 with the wafers 3 put thereon into the core tubes or heating furnaces 4A, 4B and 4C or take them out therefrom, the boats 20 are slid on the inner surfaces of the core tubes.
For this reason, impurities adhered to the inner surfaces of the core tubes are flown up and the wafers are contaminated thereby. This leads to the lowering of the yield of the semiconductor elements.